1. Field of the Invention
This invention relates generally to civil engineering and more particularly to the construction of pipelines layed into ground trenches or placed on piers.
2. Description of the Prior Art
Wide application for pipeline transmission have found pipelines made up of pipe lengths or sections hermetically interconnected. Pipe sections are joined either by welding or by using flanged fittings. A pipeline made up of weld-joined pipe sections suffers from a disadvantage due to that welding damages pipe insulation resulting in subsequent corrosion and failure of the pipeline.
On the other hand, a pipeline made up of separate pipe sections joined by flanged fittings is prone to failure at high pressures, and is normally designed to operate at a pressure range of between 0.2 and 1.0 MPa. Therefore, operation of this pipeline is accompanied by a tendency of the pipe joints to leak.
Another major disadvantage of the pipeline so constructed is in that it is not amenable to automatic pipeline laying.
One procedure indispensable from constructing pipeline with outer insulation is the application of such outer insulation coating to pipe joints on the pipeline route site.
There is known a technique for applying coatings to outer pipeline surface by spraying. Special machines have been designed for this purpose capable of cleaning the pipeline surface, heating the pipe and applying insulation to pipe joints. A machine of this type has been initially field-tested in 1973 (cf., Poljansky R. P. and Pasternak V. I. "Truby dlja neftjanoi i gazovoi promyshlennosti az rubezhom", in Russian, the "Nedra" Publishers, Moscow, p. 201, 1979).
For applying coatings to the inner surface of pipelines by spraying "in-situ", a range of machines have been developed. Such coating application operations involve, for example, injecting epoxide compounds to the interior of the pipe from both ends thereof (cf., the above publication, pp. 201 and 202).
There are known tape- or belt-type coatings used both for insulating the length of pipe and pipe joints, as well as for repairing outer insulation applied to the pipeline longitudinal seam (cf., U.S. Pat. No. 3,600,793, published Aug. 24, 1971).
Inherent in the aforedescribed constructions and techniques is a disadvantage due to low efficiency of pipeline laying and insufficient reliability of pressure-sealing more particularly, flanged fitting and gasket-type pipe joining fails to withstand skewing and water hammer effects during pipeline operation, whereas joining the pipe sections by welding requires a high degree of accuracy.
There is also known a pipeline laying method including the steps of digging a trench, joining separate pipe sections together by welding, applying an outer insulation, and lowering the pipeline into the trench.
However, this method suffers from a disadvantage because no insulation is applied to the inner surface of the pipeline resulting in reduced reliability and shorter service life of the pipeline. Another disadvantage is that the pipeline laying procedure is not automated.
There is further known a method of pipeline laying wherein a trench is dug and the pipe sections are joined by means of a binder and couplings, after which the trench is backfilled with soil (cf., USSR Inventor's Certificate No. 870,839, published 1979).
A disadvantage of the above method is that the pipeline laying operation is not amenable to automation. In addition, the joints between pipe sections fail to withstand high pressure.
There is widely known an apparatus for connecting steel pipes into a pipeline, such as a pipe welding machine.
However, this machine is likewise disadvantageous because it cannot be used for connecting pipes fabricated from such different materials as reinforced concrete, steel, ceramics, and the like. Also, the pipeline laying operation is not automatic.